I think hillstream loaches are really cool. I have one right now and I love watching him shuffle around the tank. That being said, there is a chance if you have 2 in a small tank, that one might end up bullying the other one.
Here is a paragraph regarding this point:
How many hillstream loaches can be kept together? Most people only get one because they’re more expensive and can cost around $15 each. We recommend getting just one or a group of three or more. If you get two, the stronger one may bully the weaker one over food or territory. Males like to scuffle with each other, circling round and round trying to get on top of their opponent, but no bodily harm is done. To reduce aggression levels, make sure to provide more decorations or aquarium plants to block line of sight.
https://www.aquariumcoop.com/blogs/aquarium/hillstream-loaches#:~:text=We recommend getting just one,no bodily harm is done